New "autopilot" features, designed for cars built after September 2014, will be available for customers in the United States, Tesla said. European and Asian owners must wait another week. Tesla will provide the features through an over-the-air upgrade.

Musk cautioned that autopilot functionality was in beta mode and full "hands-off" driving was not recommended.

"We're being especially cautious at this stage so we're advising drivers to keep their hands on the wheel just in case," Musk told reporters at the company's Silicon Valley headquarters. "Over time there will not be a need to have your hands on the wheel."

Reporters who took Model S sedans with the new features for a test drive and took their hands off the wheel saw a notice saying "hold steering wheel" illuminate on the dashboard.

In more difficult navigating conditions, an audio alert will come on and if that also is ignored, the car will slow and eventually stop, Tesla said.

For drivers, "We're very clearly saying this is not a case of abdicating responsibility," Musk said. "That will come at some point in the future but ... this is still early days."

Instructions to owners say "autosteer is a hands-on feature. You must keep your hands on the steering wheel at all times."

Tesla, which this month unveiled its Model X SUV, has been the U.S. pioneer in luxury electric cars charged by batteries. Its expertise in software has made it a leader in self-driving features, which more traditional carmakers have been slower to develop.

Musk estimated that within three years, cars will be able to drive "from your driveway to work without you touching anything," but regulatory approval could take years.

He said regulators would need data showing that self-driving cars work.

Teslas already on the road will help the autopilot constantly improve and become more reliable, he said.

"The whole Tesla fleet acts like a network. When one car learns something they all learn it," he said. "As ... more people enable autopilot, the information about how to drive is uploaded to the network. Each driver is effectively an expert trainer in how the autopilot should work."